Vol. 672
6. Insterstellar and circumstellar matter

Galactic population synthesis of radioactive nucleosynthesis ejecta

by T. Siegert, M. M. M. Pleintinger, R. Diehl, M. G. H. Krause, J. Greiner, and C. Weinberger 2023, A&A, 672, A54

The projected (line-of-sight) distributions of the short-lived radioactive nuclei 26Al and 60Fe have been detected in the Galactic interstellar medium with gamma-ray satellite observations from COMPTEL and INTEGRAL/SPI. This paper is a clever global simulation of those maps, using a range of formal representations for the spatial distribution of star formation (combinations of radial exponential profiles and spiral structure imposed on a disk) and with careful rendering of the underlying sources and their stochastic variability. While this is not ab initio modeling, the details of the in-out processes have been individually evaluated before being combined with a population synthesis at the Galactic level. A particularly attractive feature of this approach is that the lifetimes of the two species are so short that large-scale redistribution from macroscale dynamics within the interstellar medium is not a major concern. Therefore, unlike pre-solar grains, the simulations can exploit the "snapshot" approach to obtain a statistically consistent sky distribution. The authors find that a spiral-dominated disk (with a weak exponential radial dependence) with a scale height of about 0.7 kpc and a moderate star formation rate, about 8 M_sun yr, provides the best fit. This approach should encourage more detailed modeling and communication between the different specialties regarding Galactic chemical and population evolution.